Micromotor in a ceramic substrate

ABSTRACT

A micromotor in a ceramic substrate, including a unitary ceramic body providing a micromotor substrate which has been formed with a first internal cavity and a plurality of second internal cavities and a recess, a ferromagnetic stator formed in the first internal cavity, and embedded conductive coil structures formed in the second internal cavities and disposed in operative relationship to the ferromagnetic stator, and a rotor mechanism mounted in the recess and in operative relationship to the ferromagnetic stator and having a rotor member formed of a hard magnetic material which is free to rotate so that when voltages are applied to the coil structures, a field is created through the ferromagnetic stator which provides a torque to the rotor member causing it to rotate.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned U.S. patent application Ser. Nos. 08/868,210, filed concurrently herewith, entitled "A Method for Making a Micromotor in a Ceramic Substrate by Ghosh et al; 08/798,694 filed Jan. 29, 1997, entitled "A Method for Making a Microceramic Optical Shutter" by Ghosh et al; 08/808,896 filed Jan. 30, 1997, entitled "A Method of Making a Microceramic Electromagnetic Light Shutter" by Ghosh et al; 08/798,080 filed Feb. 12, 1997, entitled "A Microceramic Optical Shutter" by Furlani et al; 08/808,897 filed Feb. 28, 1997, entitled "A Microceramic Electromagnetic Light Shutter" by Furlani et al; and 08/820,064, filed Mar. 18, 1997, entitled "Microceramic Linear Actuator" by Furlani et al, the teachings of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a micromotor in a ceramic substrate.

BACKGROUND OF THE INVENTION

Electromechanical motors are well known in the art and have been used in a number of motion and control applications. It is, of course, highly advantageous to miniaturize such motors. Conventional motors are typically greater that I cubic centimeter in volume. The materials and methods for the fabrication of these motors are inadequate for the fabrication of microelectromechanical motors which are less than I cubic centimeter in volume.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide miniaturized motors which are less than 1 cubic centimeter in volume.

This object is achieved in a micromotor in a ceramic substrate, comprising:

(a) a unitary ceramic body providing a micromotor substrate which has been formed with a first internal cavity and a plurality of second internal cavities and a recess, a ferromagnetic stator formed in the first internal cavity, and embedded conductive coil structures formed in the second internal cavities and disposed in operative relationship to the ferromagnetic stator, and;

(b) a rotor mechanism mounted in the recess and in operative relationship to the ferromagnetic stator and having a rotor member formed of a hard magnetic material which is free to rotate so that when voltages are applied to the embedded conductive coil structures, a field is created through the ferromagnetic stator which provides a torque to the rotor member causing it to rotate.

It is a feature of the present invention that miniaturized motors can be fabricated using micromolded ceramic technology.

Micromotors have a number of advantages; they can withstand harsh corrosive or high temperature environments. Another feature of this invention is that by using micromolded ceramic technology, motors can be made in high volume with high yields at reduced cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of a sacrificial stator core of a motor in accordance with the present invention;

FIG. 2 is a perspective of one of the sacrificial stator core teeth shown in FIG. 1, with a tape cast ceramic material wrapped around its central portion, and a sacrificial fiber wound in a helical fashion on the tape cast material;

FIG. 3 is a perspective of a micromolded ceramic bottom portion which forms the base element of a microceramic motor in accordance with the present invention;

FIG. 4a is a top view of a micromolded ceramic top portion of the present invention;

FIG. 4b shows a cross-sectional view of the top portion of FIG. 4a taken along line A--A in FIG. 4a;

FIG. 5a is a perspective of an assembled motor body prior to sintering;

FIG. 5b is a perspective of an insert member which when inserted into the assembled motor mechanism of FIG. 5a provides a bearing surface;

FIG. 5c is a cross-sectional view of the insert member taken along the line B--B of FIG. Sb;

FIG. 6 is a perspective of the structure in FIG. 5a shown after sintering and etching processing and also showing apparatus mounted for filling internal cavities that result from etching away embedded sacrificial members;

FIG. 7 is a top view of the structure in FIG. 6 after all internal coil receiving cavities and the internal stator receiving cavity have been filled;

FIG. 8 is an internal cross-sectional view of the structure shown in FIG. 7 showing the internal coil and stator structures;

FIG. 9 is a perspective of the assembled motor with attached power source and controller, and;

FIG. 10a is an exploded view of the rotor mechanism, and;

FIG. 10b is a cross-sectional view of the top plug of the rotor mechanism of FIG. 10a taken along line C--C of FIG. 10a, and;

FIG. 11 is a top down perspective of the rotor member of FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention involves an integrated micromotor in a ceramic substrate. The term "micro" is used to refer to the fact that the volume of the motor itself is on the order of 1 cubic millimeter and internal features within the motor have dimensions of about 100 micrometers or less.

Referring to FIG. 1, a perspective is shown of a sacrificial stator core 10 comprising a plurality (four shown) of stator teeth 20, 22, 24 and 26. The stator core 10 is made from refractory materials such as tungsten (W), molybdenum (Mo), or Tantalum (Ta).

Referring to FIG. 2, an intermediate stage of fabrication is depicted showing a perspective of stator tooth 20 of sacrificial stator core 10 after a tape cast ceramic material 30 has been wrapped around its central portion, and a sacrificial fiber 40 has been wound in a helical fashion on the tape cast material 30. The sacrificial fiber 40 is on the order of 100 microns in diameter or less and has end portions 40A and 40B. The sacrificial fiber 40 is made from refractory materials such as tungsten (W), molybdenum (Mo), or Tantalum (Ta). The stator teeth 22, 24, and 26 (not shown) are wrapped in the same fashion with a tape cast ceramic material followed by sacrificial fibers 42, 44, and 46, respectively, having end portions 42A and 42B, 44A and 44B and 46A and 46B, respectively.

Referring to FIG. 3 a perspective is illustrated of a micromolded ceramic bottom portion 50 in the green state, with a recess 60 which is formed to receive the stator core 10 with additional space to accommodate the 22% shrinkage of the micromolded ceramic bottom portion 50 which occurs during the sintering process, and an additional recess 65. The use of the term "green" means that particulate ceramic powder, preferably mixed with an organic binder, is subjected to uniform compacting forces in order to provide an unsintered perform which has uniform density. One particular effective material is a tetragonal zirconia ceramic powder that can be micromolded to form the micromolded ceramic bottom portion 50 by standard methods such as injection molding, gel casting, tape casting, dry pressing or cold isostatic pressing. Other ceramic materials which can be used are ceramics such as Al₂ O₃, ZrO₂, AlN, BN, MgO, Al₂ O₃ --ZrO₂, SiC, Si₃ N₄ and other oxide and non-oxide ceramics and their composites thereof.

Referring to FIG. 4a a perspective is shown of a micromolded ceramic top portion 70 in the green state is shown. The micromolded ceramic top portion 70 comprises recesses 80A and 80B with respective through-holes 90A and 90B for receiving end portions 40A and 40B of sacrificial fiber 40, respectively; recesses 82A and 82B with respective through-holes 92A and 92B for receiving end portions 42A and 42B of sacrificial fiber 42, respectively; recesses 84A and 84B with respective through-holes 94A and 94B for receiving end portions 44A and 44B of sacrificial fiber 44, respectively; and recesses 86A and 86B with respective through-holes 96A and 96B for receiving end portions 46A and 46B of sacrificial fiber 46. The micromolded ceramic top portion 70 has a central through-hole 100, and additional through-holes 110 and 120 as shown. FIG. 4b illustrates a cross-sectional view of the micromolded ceramic top portion 70 taken along line A--A of FIG. 4a. Features like through-holes and recesses can be formed in the green stage by incorporating those features in the mold. Approximately, 20% to 50% larger features must be made to account for shrinkage during sintering. The amount of shrinkage depends on the relative amount of organic binders in the ceramic mixture. Typically, 2% to 5% by weight organic binders are added for compaction processes such as cold isostatic pressing and dry pressing. On the other hand, 10% to 40% by weight organic binders are added for compaction processes such as gel casting, tape casting and injection molding.

Referring to FIG. 5a, a perspective is illustrated of the assembled ceramic body 200 in which the micromolded ceramic top portion 70 is placed on the micromolded ceramic bottom portion 50. The end portions 40A and 40B of sacrificial fiber 40 are drawn through holes 90A and 90B, respectively; the end portions 42A and 42B of sacrificial fiber 42 are drawn through holes 92A and 92B, respectively; the end portions 44A and 44B of sacrificial fiber 44 are drawn through holes 94A and 94B, respectively, and the end portions 46A and 46B of sacrificial fiber 46 are drawn through holes 96A and 96B, respectively. It is instructive to note that upon assembly of ceramic body 200, through-hole 100 of micromolded ceramic top portion 70 aligns with recess 65 of micromolded ceramic bottom portion 50 forming recess 65, and through-holes 110 and 120 in micromolded ceramic top portion 70 align with stator teeth 22 and 26 of sacrificial stator core 10, respectively. FIG. 5b, illustrates a green ceramic insert 420 comprising MoSi₂ or ZrB₂. The insert 420 is placed in recess 65. FIG. 5c illustrates a cross-sectional view of the insert sectioned taken along the lines B--B in FIG. 5b.

Once assembled, the assembled ceramic body 200 is sintered in vacuum or in a controlled oxygen-free atmosphere at about 1300° to 1600° C., to form a unitary ceramic body 220 which is a ceramic substrate for the micromotor. After this sintering step, the sacrificial stator core 10 and sacrificial fibers 40, 42, 44 and 46 are etched away using Ammonium Hydroxide NH₄ OH or Hydrocloric acid leaving a first internal cavity and a plurality of second internal cavities in their place, respectively. More particularly by etching through the through-holes 90A and 90B, 92A and 92B, 94A and 94B, and 96A and 96B, the sacrificial fibers 40, 42, 44 and 46 are removed to thereby provide a plurality of internal coil receiving cavities, respectively, and by etching through the through holes 110 and 120 the sacrificial stator core 10 is removed to provide a cavity for receiving the ferromagnetic stator member. The construction of embedded structures can also be achieved by molding the green ceramic with a sacrificial plastic members. These sacrificial plastic members burn off during sintering in air. The procedure of providing embedded coils in ceramic body has been described in details by commonly assigned U.S. patent application Ser. No. 08/775,523, filed Jan. 2, 1997, entitled "Miniature Molded Ceramic Devices Having Embedded Spiral Coils" by Chattetjee et al, and commonly assigned U.S. pat. application Ser. No. 08/775,524 filed Jan. 2, 1997, entitled "Method for Forming Molded Ceramic Devices Having Embedded Spiral Coils", by Chatterjee et al, the teachings of which are incorporated herein by reference.

Referring to FIG. 6, a perspective is shown of the unitary ceramic body 220 in an intermediate stage of fabrication after the sacrificial fibers sacrificial fibers 40, 42, 44 and 46, and sacrificial stator core 10 have been etched away and apparatus have been mounted for filling the embedded cavities that result from the removal of sacrificial fiber 40 and sacrificial stator core 10. Specifically, nonporous containment structures (dams) 240 and 250 are mounted around through-holes 90A, and 110, respectively. Vacuum chamber structures 260 and 270 are mounted around through-holes 90B and 120, respectively. Containment structure 240 is filed with a molten pool of conductive metal alloy such as Au, Ag, Ag--Cu, or Cu--Sn or alternatively a thin film conductive paste. A vacuum is applied to vacuum chamber structures 260 so as to the draw conductive metal alloy into the embedded etched path connecting through holes 90A and 90B thereby forming an embedded conductive coil structure 180 in the form of wound sacrificial fiber 40 (see FIG. 1) within unitary ceramic body 220 with terminal ends in the form of conductive pads 140A and 140B (shown in FIGS. 7 and 8). This same procedure is used to form embedded conductive coil structures 182, 184, and 186 in the form of sacrificial fibers 42, 44, 46 with terminal ends 142A and 142B, 144A and 144B, and 146A and 146B, respectively (see FIGS. 7 and 8).

Containment structure 250 is filed with a molten pool soft-magnetic alloy such as NiFe. A vacuum is applied to vacuum chamber structures 270 so as to the draw soft-magnetic alloy into the embedded etched path connecting through holes 110 and 120 thereby forming an embedded ferromagnetic stator 190 in the form of sacrificial stator core 10 (see FIG. 1) within unitary ceramic body 220 (see FIG. 8).

Referring to FIG. 7, a top view of the structure in FIG. 6 is shown after all internal coil receiving cavities and the internal stator receiving cavity have been filled. Specifically, conductive pads 140A and 140B, 142A and 142B, 144A and 144B, and 146A and 146B are shown. These form the terminal ends of embedded conductive coil structures 180, 182, 184, and 186 in the form of sacrificial fibers 40, 42, 44, and 46, respectively (see FIG. 8).

Referring to FIG. 8 an internal cross-sectional view of the structure shown in FIG. 7 is depicted showing the embedded conductive coil structures 180, 182, 184, and 186 and the ferromagnetic stator 190 with ferromagnetic stator teeth 192, 194, 196 and 198.

Referring to FIG. 9 a perspective is shown of an assembled motor, an external power source 300 and a controller 310. The power source 300 supplies power to the controller 310 through connecting wires 320A and 320B. The controller 310 supplies current to the embedded conductive coil structures 180, 182, 184, and 186 through conductive pads 140A and 140B, 142A and 142B, 144A and 144B, and 146A and 146B via connecting wires 340A and 340B, 342A and 342B, 344A and 344B, and 346A and 346B, respectively. To drive the motor, controller 310 supplies current to the embedded conductive coil structures 180, 182, 184, and 186 in a synchronous fashion, thereby creating a magnetic field in the ferromagnetic stator 190 which, in turn, creates magnetic fields between neighboring ferromagnetic stator teeth 192, 194, 196 and 198 in a synchronous fashion which, in turn, interact with the magnetic field of the permanent magnet rotor member 440 causing it to rotate as is well known (see, for example, "Permanent Magnets and Brushless DC Motors," by T. Kenjo and S. Nagamori, Oxford University Press, 1984).

Referring to FIG. 10, an exploded view of rotor mechanism 400 is shown. Rotor mechanism 400 comprises a low friction ceramic insert 420, a rotor member 440 with shaft 446, and a top plug 450. The ceramic insert 420, which is an integral part of the unitary ceramic body 220 provides a lower bearing surface for rotor member 440 for permitting rotation of rotor member 440 with shaft 446. Top plug 450, which is shrunk fit into insert 420, is supported on ledge 452, and has a low friction bearing surface 454 for rotor member 440 while at the same time confining the rotor member 440 to remain within insert 420 during rotation. The rotor member 440 is preferably made from rare earth permanent magnet materials such a neodymium-iron-boron NdFeB, and is radially polarized with alternating north and south poles around its circumference (see FIG. 11).

Referring to FIG. 11, a top down perspective of rotor member 440 is depicted which shows the polarization pattern around the circumference of rotor member 440 and the cross-section of shaft 446.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Parts List

10 sacrificial stator core

20 stator tooth

22 stator tooth

24 stator tooth

26 stator tooth

30 tape cast ceramic material

40 sacrificial fiber

40A end portion

40B end portion

42 sacrificial fiber

42A end portion

42B end portion

44 sacrificial fiber

44A end portion

44B end portion

46 sacrificial fiber

46A end portion

46B end portion

50 micromolded ceramic bottom portion

60 recess

65 recess

70 micromolded ceramic top portion

80A recess

80B recess

82A recess

82B recess

84A recess

84B recess

86A recess

86B recess

90A through-hole

90B through-hole

92A through-hole

92B through-hole

94A through-hole

94B through-hole

96A through-hole

96B through-hole

100 through-hole

110 through-hole

120 through-hole

140A conductive pad

140B conductive pad

142A conductive pad

142B conductive pad

144A conductive pad

144B conductive pad

146A conductive pad

146B conductive pad

180 embedded conductive coil structure

182 embedded conductive coil structure

184 embedded conductive coil structure

186 embedded conductive coil structure

190 ferromagnetic stator

192 ferromagnetic stator tooth

194 ferromagnetic stator tooth

196 ferromagnetic stator tooth

198 ferromagnetic stator tooth

200 assembled ceramic body

220 unitary ceramic body

240 nonporous containment structure

250 nonporous containment structure

260 vacuum chamber structure

270 vacuum chamber structure

300 power source

310 controller

320A connecting wire

320B connecting wire

340A connecting wire

340B connecting wire

342A connecting wire

342B connecting wire

344A connecting wire

344B connecting wire

346A connecting wire

346B connecting wire

400 rotor mechanism

420 insert

440 rotor member

446 shaft

448 top surface

450 top plug

452 ledge

454 bearing surface

464 recess

466 shaft 

What is claimed is:
 1. A micromotor in a ceramic substrate, comprising:(a) a unitary ceramic body providing a micromotor substrate which has been formed with a first internal cavity and a plurality of second internal cavities and a recess, a ferromagnetic stator located in the first internal cavity, and embedded conductive coil structures formed in the second internal cavities and disposed in operative relationship to the ferromagnetic stator, and; (b) a rotor mechanism mounted in the recess and in operative relationship to the ferromagnetic stator and having a rotor member formed of a hard magnetic material which is free to rotate so that when voltages are applied to embedded conductive coil structures, a field is created through the ferromagnetic stator which provides a torque to the rotor member causing it to rotate.
 2. A micromotor in a ceramic substrate according to claim 1 wherein the rotor mechanism includes an insert member which provides a bearing surface for the rotor member.
 3. A micromotor in a ceramic substrate according to claim 1 wherein the ferromagnetic stator has a plurality of teeth with the embedded conductive coil structures being wound around such teeth.
 4. A micromotor in a ceramic substrate according to claim 1 wherein the rotor member is made from rare-earth permanent magnet materials including neodymium-iron-boron and further including a shaft fixed to the rotor member.
 5. A micromotor in a ceramic substrate according to claim 1 wherein the insert member is made from low friction ceramic material including MoSi₂ or ZrB₂.
 6. A motor assembly comprising:(a) a micromotor in a ceramic substrate having:(i) a unitary ceramic body providing a micromotor substrate which has been formed with a first internal cavity and a plurality of second internal cavities and a recess, a ferromagnetic stator located in the first internal cavity, and embedded conductive coil structures formed in the second internal cavities and disposed in operative relationship to the ferromagnetic stator; (ii) a rotor mechanism mounted in the recess and in operative relationship to the ferromagnetic stator and having a rotor member formed of a hard magnetic material which is free to rotate so that when voltages are applied to embedded conductive coil structures, a field is created through the ferromagnetic stator which provides a torque to the rotor member causing it to rotate; (b) a power supply; and (c) means connected to the power supply for selectively applying voltages to the embedded conductive coil structures to cause the rotor member to rotate.
 7. A motor assembly according to claim 6 wherein the rotor mechanism includes an insert member which provides a bearing surface for the rotor member.
 8. A motor assembly according to claim 6 wherein the ferromagnetic stator has a plurality of teeth with the embedded conductive coil structures being wound around such teeth.
 9. A motor assembly according to claim 6 wherein the rotor member is made from rare-earth permanent magnet materials including neodymium-iron-boron and further including a shaft fixed to the rotor member.
 10. A motor assembly according to claim 6 wherein the insert member is made from low friction ceramic material including MoSi₂ or ZrB₂. 